The present invention relates to an image data compression device employed in an image data processing apparatus, such as a still video camera.
Still video cameras utilizing IC memory cards as recording media are well known, Since the IC memory card is capable of storing only a limited amount of data, the number of image frames stored as files in the IC memory card is also limited. In order to increase the number of frames in the IC memory card, the image data is compressed in accordance with a compressing algorithm, and then, the compressed image data is stored in the IC memory card. One such compression algorithm is the JPEG (Joint Photographic Experts Group) format, a "lossy" method.
When image data is compressed with a "lossy" compression method, however, the quality of an image reproduced from the compressed image data is not as good as the originally captured image, as minute image information is lost during the process of compression. If an image is compressed to a higher degree of compression, then more image information is lost.
In a still video camera enabling a user to select whether or not image data is compressed when the image data is stored in the IC memory card is suggested, if a user thinks it is not critical to maintain the quality of the image when the image data is stored, in the IC card memory, the user can store the image data compressed. On the other hand, if the user wishes to retain the highest possible quality, the image data can be stored uncompressed.
As the user continues to take and store photographs, the IC memory card becomes full of image data files. If the user, desires to take additional photographs, another IC memory card trusts be used. Alternatively, instead of replacing the IC memory card, the user deletes or compresses image data already stored in the IC memory card. In such a case, the user is more likely to convert a file previously stored in the IC memory card, since no previous images are lost by this solution.
However, once the image data is stored in the IC card memory, it is difficult to identify the image data contained in each file without reproducing the image from the image data on a screen or hardcopy. That is, since it is difficult for the user to identify which images should be high quality and which may be of lower quality without reproducing the images; it is difficult to select which files may be compressed or further compressed to free some of the IC card memory. As described above, if the image data of an image that the user wishes to retain at a higher quality, already stored in the IC memory card, is compressed or further compressed, information will lost from the desired image data, and the image later reproduced from the compressed data is deteriorated.